The present invention relates to an aircraft Flight Management System (FMS),and more particularly, to an apparatus for controlling the vertical profile of a flight plan of the aircraft.
Integrated Flight Systems of todays modern commercial aircraft are operated under the jurisdiction of a Flight Management Computer and a conventional Autopilot and Autothrottle, well known to those skilled in the art. The Flight Management Computer identifies the correct route (flightplanning), identifies current aircraft position (navigation), and selects aircraft altitude, speed, vertical speed, thrust and heading such that the aircraft follows the desired route (guidance). The conventional Autopilot dynamically adjusts the aircraft control surfaces and throttles to maintain the guidance targets (control).
The FMS performs the task of flightplanning by compiling a four-dimensional route, defined by a Lateral Flightplan, a Vertical Flightplan and an Elapsed Time Trajectory. These flightplans are compiled from stored Navigation Data Bases and flight-crew entries. The FMS performs the task of navigation by identifying aircraft position relative to fixed points on the surface of the earth. A lateral position, vertical position and elapsed time are computed by a combination of data from ground-based transponding radios, radar, and aircraft motion sensors. The FMS performs the task of guidance by determining the appropriate altitude, speed, thrust, and heading required to maintain the current leg of the flightplan. These targets are determined by a comparison of aircraft position (navigation) to the desired profile (flightplanning) and may take into account temporary deviations from the flightplan due to weather, traffic equipment failure or on-board emergencies. The Autopilot controls the aircraft by adjusting the pitch, roll and yaw control surfaces and the throttle position, to instantaneously maintain the desired aircraft trajectory defined by FMS guidance.
The existing Flight Management Systems have successfully automated the flightplanning, navigation, lateral guidance and control tasks. The exception, the task of vertical guidance (i.e., the FMS control of the vertical profile) has not been included in the FMS control.
The successful automation of the flightplanning, navigation, lateral guidance and control tasks can be attributed to the existence of explicit and comprehensive procedures, rules and equations that describe the necessary computations or desired aircraft behavior for lateral guidance (delineated in ARINC Specifications and FAA Advisory Circulars). These procedures, rules and equations, applied in a coordinated manner by Air Traffic Control (ATC) and flight-crews, can be used to generate properly functioning algorithms for implementation in automated systems.
By analogy, the lack of success in the automation of the vertical guidance task can be attributed to the absence of explicit, comprehensive and universally accepted procedures for flight management of the vertical profile. The absence of these procedures, is evident in the lack of coordination between ATC, flight-crews and the semi-automated systems that require flight-crew intervention, and results in an increase in cockpit workload. In addition, the existing automated systems (built based on an incomplete set of procedures and using the nested if-then-else algorithms of conventional structured programming) are difficult to design, unmanageable, and difficult to modify (to support evolving designs) with integrity.
The present invention relates to an improved apparatus for the automation of vertical guidance that overcomes the drawbacks of existing systems by:
1) the creation of a comprehensive and universally acceptable set of procedures (known as Vertical Guidance Operational Procedures) for flight management of the vertical profile by Air Traffic Control, flight-crews and system design engineers, and PA1 2) the automation of the Vertical Guidance Operational Procedures via a unique set of control law algorithms that utilize the techniques of closed-loop feedback and a knowledge-based decision construct. (These operational procedures represent a collation of international airspace regulations, air traffic control policies, airline/flight-crew policies and the operational limits of the aircraft.)
The vertical plane (i.e., the vertical profile of an aircraft or vertical axis control) may be considered as having two dimensions, altitude (up/down) and time (speed). The vertical profile of the aircraft is controlled via the elevators and the engines--the pitch (up/down) components and thrust components, respectively. In present day systems, the throttle (thrust) provides one trajectory for the vertical control function, and the elevators provide another trajectory for the vertical control function. Generally, the control functions of these present day systems are being performed in a serial fashion and often times these control functions are said to be coupled, and oppose one another.
Thus, there is a need to coordinate the elevator/throttle control. The present invention selects targets and control modes such that the elevator control and the throttle control are coordinated thereby resulting in an integrated control of the vertical flight profile, i.e., of the elevator command and the throttle command.